It's a difficult one to call. As you know, the Buying a new camera... forum is intended only for those who are undecided on the brand. If a member already knows they want, say, a Pentax but can't decide which one then they should post in the Pentax forum.

By the same token, any member trying to decide on a lens for a Pentax should ideally also post in the Pentax forum. We do get into a grey area when a member is considering a type of lens for a Pentax, for example a short zoom. It makes sense to discuss any third party offerings, such as a Sigma, in the Pentax forum, to continue with the example. Unfortunately, that leaves the Sigma forum rather unpopulated. The same is even truer for the Tamron forum as, unlike Sigma, there aren't any cameras to discuss there.

Luckily, I don't have any special voice in such a decision. My own personal view is that because we buy lenses for cameras we already own then specific questions should be raised in the camera manufacturer's forum. And, of course, if the various lens systems are part of trying to choose a brand when buying a new camera then the Buying a new camera... forum is exactly the right place for questions.

We do see conversations which are more general in nature but once you have pigeon-holed questions about suitability of different types of lenses into the various Photography tips forums, which are to "Share your tips or ask questions about xyz", there isn't a lot left over. In another thread I wondered whether a "Lens talk" forum would be useful as those "left over" conversations tend to get split equally between Comments and feedback and Off-topic and, really inappropriately given the forum guideline, the Lens Gallery. The difficulty would be that if Gordon decided to implement a "Lens talk" or a "Buying a new lens" forum we would end up with some posts in that forum and other posts, quite possibly asking exactly the same question, in the relevant manufacturer's forum. That makes the whole CameraLabs forum a much less friendly place for members (and lurkers) to find specific answers from earlier conversations. As I said at the start, it's a difficult one to call.

maybe it could be an idea to split the forum into the different systems?
you'd get
-canon
-nikon
-sony
-fourthirds
might make more sense, since most likely the questions on the olympus forum would be about lenses (though admittedly not all)
it's a difficult call i guess...

Hmmm, it's an interesting idea, but as Bob says, if you're after a lens for a particular system, then post in that manufacturer's forum.

If you have a general lens question, you could always post in the buying a new camera section. But since the selections vary between systems, we'd soon end up in the manufacturer's own forum for relevant options...